I discovered that:
When Opera Turbo is enabled, webpages are compressed via Opera's servers so that they use much less data than the originals. This means that there is less to download, so you can see your webpages more quickly.
This includes images, so maybe I need to look into this more.

My other websites don't problems with Opera in turbo mode.
So could be type of images I use (GIF, PNG instead of JPG).